Method of reacting felted cellulose, sulphate cellulose and sulphite cellulose with gseous ketenes



Unite States Organic fibrous materials tend to adsorb moisture until the moisture content is in equilibrium with the moisture content of the surrounding air. The adsorption and liberation of moisture may be retarded by coating the fibres with bituminous or other plastic materials but such coating is substantially without influence upon the finally resulting moisture content of the fibrous material resulting from the adsorption of moisture vapors.

The adsorption of moisture in fibrous material is accompanied by swelling, i.e. an increase in volume, whereas liberation of moisture produces a decrease in volume. Consequently, materials containing organic fibres, when in practical use, are never stable but Work, i.e. expand and retract, according to the alterations in the moisture content and temperature of the surrounding atmosphere.

Since swelling is substantially an increase in cross section of the individual fibres, a spun thread or yarn will retract longitudinally upon swelling of its fibres. Objects produced from such threads or yarns will accordingly shrink as the result of an increase in the moisture content thereof. On the contrary, felted materials such as paper, cardboard and sheets will increase their dimensions in all directions upon an increase in the moisture content thereof This property of fibrous materials is frequently a considerable disadvantage in their practical use, even in those cases Where the fibrous material is impregnated with Water-proofing substances, such as bitumen, for instance in the case of bituminous roofing and insulating materials. When producing such materials, felt is impregnated with bitumen at an elevated temperature so that the fibres are quite dry. After such materials have been applied to a roof, for instance, the fibres take up moisture and swell which causes the roofing to bulge out, particularly in rainy or humid weather. This bulging may cause the felt to tear loose at the overlaps whereby leaks in the roof will result. Even though the moisture will partially escape from the felt in dry weather, whereby bulging diminishes, any leaks that may have been previously produced will not heal. Moreover, when roofing felt having a high content of moisture is suddenly exposed to hot weather and strong sun, especially on roofs facing toward the south, it may tend to blister, as the vapour pressure inside the material is increased and the bituminous material is at the same time soft.

For the above and other reasons there is a great need for a method of treating felted fibrous sheet material containing cellulose fibres so as to stabilize the material against the influence of moisture vapors.

It is known to expose fibrous materials to mechanical compression and to seek to stabilize the volume of such materials, with or without previous compression, by ad'- hering together the fibres with urea or melamine formaldehyde resins, but such methods have not been successful for the stated purpose, since the materials thus treated are still capable of adsorbing moisture Vapors, just as in the case of the materials treated with bitumen mentioned above.

atcnt 3,051,543 Patented Aug. 28, 1962 wherein R and R designate hydrogen or alkyl. Thus,the ketene reacts with alcoholic groups to form esters, with carboxylic groups to form mixed anhydrides, with amino groups to form amides etc. The reaction of ketene with cellulose, which contains a number of alcoholic groups with which the ketene may react in accordance with the above named formula, has heretofore been described, only as being carried out in the presence of a liquid phase, for instance, ether, benzene or glacial acetic acid, mostly for the purpose of producing liquid or plastic products for use in the production of artificial spinning materials or raw materials for the plastic or lacquer industries.

A particular known process for the treatment of fibrous products involves the treatment of the latter with ketenes containing long alkyl chains for the purpose of rendering the fibrous products hydrophobic and, particularly, waterrepellent known process consists in dissolving the ketenes, which are solids, in an organic solvent in which the fibrous product is dipped after which it is dried and subjected to a temperature slightly exceeding C., whereby the desired impregnation is obtained. In this process, the fibres, as a whole, practically retain their original composition, since very few scattered reactive groups react chemically with the ketene. On account of the hydrophobic character of the long chain hydrocarbon residues contained in the ketene, the admission of water in the liquid form to the interior of the product is inhibited whereas the material as a whole will retain an unchanged or nearly unchanged capacity for adsorbing moisture vapour.

As distinguished from the above, it is an object of the process according to the present invention to transform the entire material so that, not only its capacity of adsorbing liquid moisture, but also its capacity for adsorbing moisture vapors, irrespective of the duration of the influence of moisture, and also other properties of the material, are appreciably or even very radically changed.

It has now been found that the above object can be attained, and that the strength may at the same time to be improved, when a felted fibrous sheet material containing cellulose fibres from the class consisting of fibres of cellulose rags, sulphate cellulose and sulphite cellulose, is subjected to treatment with a gaseous low molecular ketene under such conditions that the fibrous form is maintained but the weight of the material is increased as a consequence of achemical reaction of the constituents thereof with the ketene.

The preferred manner of treating the fibrous material with a gaseous low molecular ketene consists in exposing the material in a substantially dry state, at a temperature at which the desired amount of reaction can take place in a reasonable time, to a gaseous atmosphere consisting of or containing the gaseous ketene, and discontinuing the exposure when the. desired increase in weight has been obtained. The influences of the individual factors and conditions prevailing during the reaction, of the kind of raw material employed and of the time of reaction are discussed in considerable detail hereinafter in order to enable a person skilled in the art to obtain the desired product when carrying out the process.

In the following Table I, the changes in the tensile strength, adsorption of water vapour, increase in length .and moisture contents of various materials. are given for various amounts of ketene introduced into the materials by the process in question.

TABLE I The Properties of Ketene-Treated Materials Increase in length in me. on changing the relative moisture of the atmosphere from to 93 percent Machining direction Increase Material in weight Adsorption Tensile strength in kiloof water grams per cm. atvapour in percent on dry weight at 93 per- 52 percent cent relarel. moiswet tive moisture ture in atmosphere Rag pulp 600 grams per sq. m..

along Sulphate pulp 500 grs. per sq. m-.

alon o Forms"--.

Sulphite pulp 125 grs. per sq. m

alon

, The values given for increase in length, adsorption and tensile strength are averages determined graphically.

It is apparent from 'Table I that the increase in dimensions both along and across the manufacturing direction (and consequently the changes in volume) decrease with increasing amounts of ketene introduced into the material. This elfect is appreciable even in the case of the smallest amount of ketene introduced into the material (5 percent). On the. other hand, with the greatest amount of introduced ketene, recorded in the table, the effectis so considerable that the increase in length amounts to a fraction only of the increase in length of the untreated material. The same thing applies to the adsorption of water. -='Ihe increase in tensile strength is considerable even with ordinary moisture contents in the air, and increases in the tensile strength of a wet material amount to a multiple of that of the untreated material. a

The improvementis achieved not only with materials consisting wholly of cellulose fibres, but also with materials which contain animal fibres in addition to. the cellulose fibres, for instance materials made from ragcontaining pulp. 1' he treatment with gaseous low molecular ketene also favorably influences certain artificial fibres, for instance those of polyvinyl alcohol or viscose.

As a result of the treatment with gaseous low molecular ketene, felted materials consisting of or containing cellulose fibres, for instance paper or board, increase both in weight and volume. Thus, for instance, in theproduction of a roofing felt corresponding to those hitherto in use and having a basic, weight of 600 grs. per square meter, it is possible to use, as the starting material, a felt. weighing 500 grs. per square meter and to treat it with ketene until its weight is increased to 600 grs. per square meter. The thickness of the resulting felt will then equal the thickness of the usual felt weighing 600 grs. per square meter, whereas the tensile strength will equal that of the usual felt Weighing 650 grs. per square meter, and the adsorption of moisture will equal that of a conventional felt weighing only approximately 350 grams per square meter. While the swelling due to moisture vapor adsorption has been reduced by /3, the felt has retained the same capability of adsorbing bitumen as an untreated felt.

The treatment with ketene can be carried out according to the present invention using pre-formed fibrous sheet material, for instance in the form of felt, paper, cardboard or plates. The ketene treatment can easily be carried out continuously, since such fibrous sheet materials are often available in the form of continuous sheets or webs. Moreover, the treatment with ketene can easily be fitted into the manufacturing process for the sheet material, with the various fibrous raw materials incorporated in the final material being thereby treated at one and the same time.

The treatment with ketene may also be carried out on the raw material which is thereafter further processed to provide the desired final material in the form of felt, paper, cardboard, plates, sheets or boards, yarn or textile materials. In this case, the raw materials may be in the form of felt, paper, plates, sheets, boards, yarn or textiles which are first treated with ketene and then converted, in known manner, to free fibres from which the desired final fibre product may be manufactured.

Treatment carried out on the raw material is of importance when the final felted product is to contain materials which are not to be treated with ketene or are not capable of reacting with ketene, for instance cellulose acetate.

Further, the ketene treatment may also be carried out upon fibres, as such, prior to conversion of the fibres into felt, paper, cardboard, plates, sheets or boards, yarn or textile materials, and this has the advantage over the treatment of the raw material in the form of felt, paper, plates, sheets, boards, yarn or textiles, as mentioned above, in that the apparatus to be employed in the treatment with ketene can be more freely chosen.

The gaseous low molecular ketene applied according to the present invention is preferably ordinary ketene 5 CH CO, but lower homologues or polymers, for instance diketene, which are volatile or gaseous substances, can be used without difliculty. Thus, in the formula R R C: C20, R and R may be hydrogen or the same or different alkyls having 1-3 carbon atoms, provided that the groups R and R together do not have more than 4 carbon atoms.

It is not necessary to use a ketene in its pure form as it can be used in the form in which it is obtained during its manufacture or in a partially purified form or in admixture with other gases. Thus, if the ketene is produced by pyrolysis of acetone, the resulting mixtures, or mixtures derived therefrom, can be used, whether or not the unconverted acetone is removed, but provided the mixtures contain substantially only ketene and methane. The same applies to the use of ketene produced from other starting materials, for instance acetic acid. Particularly when ketenes of a comparatively high degree of purity are used, it maybe advantageous to dilute the reaction gas with, for instance, an inert gas such as nitrogen or carbon dioxide in order to control the process.

The reaction is advantageously carried out at an increased temperature in order to obtain a short reaction time. Suitable temperatures are between approximately 100 C. and approximately 250 C. The lower limit for the temperature depends on the desired reaction time which is, in turn, determined by the desired increase in weight of the material and the nature of the latter. The

reaction time at temperatures below 50 C. are usuallytoo long Whereas a reaction temperature of 100 C. is in certain cases favourable. The higher limit for the temperature depends generally on the capability of the material to endure heating.

A guide for the temperature to be used in the treatment of various materials with gaseous ketene for obtaining a desired result is to be found in the following table applicable for gaseous mixtures containing approximately 30 percent ketene.

TABLE II Ketene Absorption in Various Materials Dependent on Temperature [Time of treatment: 20 minutes] Tempera- Increase in Material ture of weight, treatment, percent 50 100 0 Cotton 150 2.0 180 9. 2 200 20.2 50 0. 4 100 0. 8 W001 150 2. 7 I 180 5. 2

50 0. 6 100 l. 9 150 5. 9 Rag pulp (cotton 75%, wool 20%, viscose 180 13. 8 200 19. 2 220 27. 7

50 0.2 Sulphate cellulose 100 1. 7 150 7. 6 200 29. 8 50 1. 5 Sulphite cellulose 100 1. 2 150 4. 9 200 19. 7 Wood pulp (newsprint) 200 27.0

1 Badly damaged. 2 Destroyed.

At a given temperature the increase in weight obtained depends substantially on the kind of material and the time of treatment. A guide for the time of treatment is contained in the following Table III applicable to the same gaseous mixture as Table II.

TABLE III Ketene Absorption in Various Materials Dependent on the Time 0 Treatment- [Ternperature 200 0.]

Time of treatment, minutes Increase in weight, percent Material Rag p p 20 Sulphate cellulose 5 Sulphite cellulose. i

Wood pulp (newsprint) 200 In the treatment of felt for bituminous roofing and insulating materials, the temperatures are preferably between about and about 250 C. and the treatment is continued until the material has absorbed from approximately 4 to 30 percent of its weight of gaseous ketene calculated as ketene (CH CO). The material thereby obtained combines to a considerable extent a reduced capability to absorb moisture vapor with favorable properties of strength, particularly in the wet condition, and at the same time it possesses the same capability of absorbing bitumen as an untreated felt material.

To illustrate the manner in which the explosure of the material to an atmosphere consisting of or containing gaseous low molecular ketene at an elevated temperature can be carried out, the following example is given.

The material to be treated is placed in a horizontal tubular container of circular cross section the length of which is twenty times its diameter. 4 of its length is surrounded by a heating jacket in which there is circulated a heating medium suitable for maintaining the desired temperature in the interior of the tube during the process. When treating small samples for experimental purposes, oil is a suitable heating medium, but, in the treatment of larger quantities of material, other heating media, such as, live or superheated steam, may be preferred. The container can be opened at one or both of its ends for inserting the material to be treated and withdrawing material that has been treated. Material to be treated in the form of loose fibres is introduced in baskets of metal or placed on trays. When the material to be treated is in the form of paper sheets, card boards or felts, they may be placed on grates placed within the container. Adjacent to one of the ends of the container there is an opening for admission of the ketene containing reaction mixture and, at the opposite end, there are openings for withdrawal of the mixture that has passed along the tubular container. After having introduced the material in the container and heated the jacket to the desired temperature, a gaseous mixture containing 30 percent by volume of ketene is passed through the container at a rate of 0.4-0.5 g. ketene per minute per litre of container volume.

Tables I, II and III refer to samples produced as above in a tubular container 1 meter long having an internal diameter of 50 mm.

The method may also be carried out continuously and at increased pressure if so desired in order to increase the velocity of the reaction. It is not necessary that the fibrous material be perfectly dry at the beginning of the exposure to the atmosphere consisting of or containing gaseous low molecular ketene since, in the case of ketene, the presence of moisture will only give rise to the pro duction of acetic acid, and the acetic acid which may thus be produced during the process will react with fresh ketene to form acetic acid anhydride which acts as an acetylating agent in a very similar manner to the action or ketene.

What I claim is:

Method of treating a felted fibrous sheet material containing cellulose fibres from the class consisting of fibres of cellulose rags, sulphate cellulose and sulphite cellulose to stabilize the material against the influence of moisture vapors, consisting in reacting said felted material in a substantially dry state by exposing it to a gaseous atmosphere at a temperature between approximately 100 and 250 C. and containing a gaseous low molecular ketene having the formula R R C:C:O in which R and R are selected from the group consisting of hydrogen and an alkyl group having 1.to 3 carbon atoms, and R and R together have a maximum of 4 carbon atoms, so as to react said gaseous ketene with substantial numbers of alcoholic groups, anddiscontinuing the exposure of the felted material to said gaseous ketene-containing atmosphere when said felted material has absorbed an amount of said gaseous ketene which, calculated as ketene (CH CO), increases the weight of said felted material by 4 to 30 percent, whereby said felted material has a decreased ability to absorb moisture, an increased strength and improved stability of length and volume under variable moisture conditions.

References Cited in the file of this patent UNITED STATES PATENTS 2,380,003 Whitehead July 10, 1945 2,411,860 Hentrich ,..,Dec. 3, 1946 2,629,674 Ericks Feb. 24, 1953 2,762,270. Keim etal. Sept. 11, 1956 2,798,283 Magat et a1. July 9, 1957 2,805,464 Bolmeyer et al. Sept. 10, 1957 2,810,184 Sherman Oct. 22, 1957 2,816,349 Pamm et a1 Dec. 17, 1957 FOREIGN PATENTS 158,851 Great Britain June 23, 1921 264,937 Great Britain Jan. 31, 1927 522,204 Great Britain June 12, 1940 OTHER REFERENCES Ind. and Eng. Chemistry, May 1949, pp. 1018-1021. Ott: Cellulose and Cellulose Derivatives, Part II, 2nd Edition, 1954, pp. 764 and 765. 

